Laser-equipped material working apparatus, for example, machining and welding apparatus, which can be used for precision cutting or welding operations, must apply a high beam intensity to the surface of the workpiece within a very small and very precisely and repeatably defined cross section. In many cases, as in the cutting of metals, it is also desirable to maintain one particular direction of polarization.
Usually the effort is made to satisfy these requirements by striving to construct the laser so as to produce a beam of rotation-symmetrical cross section, if possible even with a Gaussian distribution. In this manner it is possible to assure equal conditions regardless of the path to be traced on the workpiece. The requirements concerning direction of polarization are fulfilled in like manner by the introduction of a rigid mirror system which converts the linearly polarized beam emerging from the laser to a circularly polarized beam.
The need for rotational symmetry, however, in the case of high-power lasers, such as carbon dioxide lasers with a power of more than 1000 watts, can be satisfied repeatably only with great difficulty, so that the known high-power lasers are but insufficiently suitable, particularly for precise cutting operations.
It is an object of the invention, in apparatus using high-power lasers in the multi-kilowatt range, to assure an always optimum and repeatable intensity distribution and polarization adapted to the path of relative movement of the beam.